How do I delete an observation?

In the list, open the “⋯” menu on the row then “Delete”, and confirm. For several observations, tick them then “Delete”.

The observation is moved to the project's trash, not erased: find it in the “Deleted” category of the list, or in Settings → Trash, to restore it.

A completed observation you want to take out of the lists without deleting it can be “Archived” (same menu): it can still be viewed in “Archived”.